Field of the Invention
The present invention relates to a planetary gear train of an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission for a vehicle which improves power delivery performance and fuel efficiency as a consequence of achieving nine forward or more speed stages using a minimum number of constituent elements, enlarging a span of gear ratios, and linearly increasing or decreasing step ratios between speed stages.
Description of Related Art
In recent years, a rise in oil price causes dashing into unlimited competition for enhancing fuel efficiency.
As a result, a research into reduction of a weight and the enhancement of the fuel efficiency through down sizing is conducted in the case of an engine and a research for simultaneously securing operability and fuel efficiency competitiveness through multiple speed stages are conducted in the case of an automatic transmission.
However, in the automatic transmission, as the number of speed stages increases, the number of internal components increase, and as a result, mountability, cost, weight, transmission efficiency, and the like may still deteriorate.
Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components may be important in order to increase a fuel efficiency enhancement effect through the multiple speed stages.
In this aspect, in recent years, 8-speed automatic transmission tends to be implemented and the research and development of a planetary gear train capable of implementing more speed stages has also been actively conducted.
Since a span of gear ratios of the recent 8-speed automatic transmission is merely 6.5 to 7.5, the 8-speed automatic transmission has no great effect of improving fuel efficiency.
In addition, since step ratios between speed stages may not be increased or decreased linearly in a case in which a span of gear ratios of the 8-speed automatic transmission is greater than or equal to 9.0, driving efficiency of an engine and drivability of a vehicle may be deteriorated. Accordingly, there is a need for development of a high efficient automatic transmission with 9 or more forward speed stages.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.